Fume hood construction



Nov. 16, 1965 J, M. KATzFl-:Y ETAL 3,217,530

FUME HOOD CONSTRUCTION Filed Feb. 20, 1963 5 Sheets-Sheet l Jmesjfj NOV. 16, 1965 J. M. KATZFEY ETAL 3,217,530

FUME HOOD CONSTRUCTION Filed Feb. 20, 1963 5 Sheets-Sheet 2 x l. o'

INVENTORS.

Nov. 16, 1965 J. M. KATZFEY ETAL 3,217,530

FUME HOOD CONSTRUCTION Filed Feb. 20, 1965 3 Sheets-Sheet 5 INVENTORS.

L/ZtmesM/af f6 BY Le@ United States Patent 3,217,630 FUME HOOD CONSTRUCTION .lames M. Katzfey and Leo A. Puls, Two Rivers, Wis., assignors to Hamilton Manufacturing Company, Two Rivers, Wis., a corporation of Wisconsin Filed Feb. 20, 1963, SenNo. 259,991 11 Claims. (Cl. 98-115) This invention relates to fume hoods for use in chemical laboratories and the like.

It is a primary object of this invention to provide a novel fume hood having` a non-corrodable interior.

Still another object is to provide a fume hood having improved air flow characteristics within the hood.

It is another object to provide a fume hood while includes a novel baiile.

A still further object is to provide a fume hood of the foregoing character, wherein portions of the hood may be easily removed for replacement or servicing.

Still another object is to provide a fume hood having an access opening at the front and a novel sash construction for opening and closing such access opening.

Other objects and advantages of the invention will be come apparent from the following description taken in conjunction with the accompanying figures of the drawings, in which:

FIG. 1 is a fragmentary front elevational view of a fume hood embodying the invention;

FIG. 2 is a sectional viewtaken on the line 2-2 of FIG. 1;

FIG. 3 is an enlarged fragmentary sectional view taken on the line 3--3 of FIG. 2;

FIG. 4A is a fragmentary sectional view taken on the line 4-4 of FIG. 3;

FIG. 5 is an enlarged fragmentary view taken on the line 5-5 of FIG. 1;

FIG. 6 is a sectional View taken on the line 6-6 of FIG. 2;

FIG. 7 is a sectional view taken on the line 77 of FIG. 3; and

FIG. 8 is a fragmentary sectional View, similar to a portion of FIG. 3, of an alternative construction of the fume hood.

In general, a fume hood embodying the invention comprises a structure adapted to be positioned on a suitable base. To prevent damage by corrosive fumes generated within the hood, the latter is constructed such that the portion of its interior exposed to the fumes is `made exclusively of noncorrodafble material. An access opening to admit air to the hood and an exhaust opening to withdraw fumes from the hood are formed` in the hood, and a non-corrodable baille is pivotally mounted within the hood between these two openings to regulate the ow of air from the access opening to the exhaust opening. A sash assembly may be provided for closing the access opening, and a light assembly may be mounted within the hood for illuminating its interior. The portions of the sash and the light assembly exposed to corrosive fumes are also formed exclusively of noncorrodable material. Further, the hood is constructed such that portions of it may be easily removed, for maintenance purposes.

In greater detail, the fume hood, shown in FIGS. l to 5 and indicated generally by the numeral 10 is adapted to be mounted on a base 11 (FIG. 2) which may be a cabinet or, in the case of walk-in fume hood, a floor. The hood comprises a top wall 12, a front Wall 13, a back wall 14, and two side walls 16 and 17 which are joined together to form a hollow lbox-like structure.

Each side wall 16 and 17 comprises a generally rectangular frame member 18 made of metal and having a ice structural shape such as tube or an angle, and a side panel 19 secured to the inner side of the frame member 18. The frame member 18 and the panel 19, which is made of a non-corrodable material, are preferably bonded together. One or both of the side walls 16 and 17 may be provided with a rectangular movable section 21 (FIGS. 2 and 3) so that a person may gain access to the outside of the hood from its interior when the hood is installed with the front wall 13 flush with a laboratory wall, for example. The section 21 is held in place Within a rectangular opening 20 formed in the panel 19 by two vertical cleats 22 and 23, an upper cleat 24 and a lower cleat 25. The vertical and upper cleats 22, 23 and 24 are secured to the outer surface of the panel 19, preferably by bonding, with a portion of each cleat 22 to 24 extending over the margin of the opening 20. The lower cleat 25 is secured,vpreferably by bonding, to the outer surface of the removable section 21 with a portion extending downwardly from the lower edge of the section 21 to overlap the outer surface of the panel 19, the length of the cleat 25 being such as to tit between the side cleats 22 and23 and have less than the width of the opening 20. The upper end of the section 21 is held in place by screws 26-made of a non-corrodible material such as nylon, the screws 26 being passed through openings in the section 21 and threaded into the upper cleat 24. To remove the section 21, the screws 26 are removed and the section 21 is tilted inwardly and then liftedout.

The back wall 14 comprises a rectangular back panel 28 which is secured `to rear vertical surfaces of the frame members 18 of the side walls 16 and 17as by bonding.

or by screws 29 (FIG. 3). When screws are used, they are on the outside of the hood, as shown in FIG. 3, where they are not exposed to corrosive fumes. An angular member 31 (FIGS. 2 and 3) may also be secured to the outside of the back panel 28 along its lower edge as by bonding, one portion of the angular member 31 being seated on the base 11.

The top wall comprises a top panel 32 which rests on the upper edges of the side panels 19 and the Iback panel 28, and overlies the upper horizontal surfaces of the frame members 18. Another angular member 33 (FIG. 2) may be positioned at the juncture of the back panel 28 and the top panel 32 on the outside of the back panel and is secured to these two panels as by bonding, the top panel extending rearwardly lof the back panel for this purpose. The top panel `32 is also secured to the frame members 18 as by screws or an adhesive. Further, a cir cular exhaust opening is formed in the top panel 32 adjacent the rear wall, and a cylindrical flange 34 may be provided around this opening for attachment to an exhaust duct of a conventional blower system.

The front wall 13 comprises vertical corner posts 36' and 37 adjacent the side walls 16 and 17, respectively, which support a sash assembly 38 and an air bypass grille 39 (FIGS. l and 2). Each corner post 36 and 37 comprises an attaching angle 41 (FIGS. 3 and 7) which is positioned against the vertical front and outer side surfaces` 0f the tubular frame member 18 of the adjacent side wall and is secured thereto by a plurality of nut and bolt combinations 42. Holes are formed through the frame members 18 to receive the bolts, .and the holes in the angles 41 for the bolts is preferably countersunk. A` spacer 43 is preferably positioned between each frame member 18 and angles 41. Each cornerpost furtherincludes a column `44 of stepped formation secured as `by spot welding to the outer surface of each angle 41, and an outer plate 46 secured as by welding to the column 44.

The front wall 13 further includes members secured to the cornerposts 36 and 37 and forming an access opening in the front wall. These members comprise a cover 51 secured as by screws 53 (FIG. 3) to the outer plate 46 and to the column 44 of each cornerpost, the covers 51 forming the vertical sides of the access opening. The covers 51 extend vertically from the bottom of the hood up to substantially one half its height, and each cover 51 has an inwardly slanting portion 52.

The bottom side of the access opening is formed by a foil 54 (FIGS. l and 2) which extends horizontally between the cornerposts and is secured thereto at its outer ends. The foil 54 has an upwardly and inwardly slanting portion and is spaced from the base 11 to form a lower air bypass opening 55.

The upper side of the access opening is formed by a panel 56 which extends between and is secured to the forward surfaces of the outer plates 46 of the cornerposts 36 and 37. The panel 56 also has an inwardly slanted portion adjacent its lower edge, and a rectangular opening is formed in the panel 56 which is covered by the grille 39, this opening forming an upper air by-pass opening.

As shown in FIG. 2, the forward surfaces of the covers 51, the foil 54 and the panel 56 are flush with each other and form a neat appearance. In the event the hood is equipped with accessories such as gas, hot water, etc., valves (not shown) for these accessories may be mounted behind the cornerposts on the outside of the side walls 16. Control shafts 59 having handles 60 for the valves may be mounted on the covers 51 as shown in FIG. 3.

The entire front wall 13 may be separated from the remainder of the fume hood by rst removing the screws holding the covers 51 and the panel 56, and then removing the bolts of the assemblies 42. The forward stepped portion of the column 44 of each cornerpost extends in front of the bolt assemblies 42 and an opening 58 is formed in this portion of the column in alignment with each of the bolts, so that a screwdriver may be inserted through the openings 58 and engage the bolts.

The sash assembly 38 comprises a sash 61 slidably mounted between the cornerposts 36 and 37, and means for counterbalancing the weight of the sash 61. The sash 61 comprises a rectangular glass pane 62 enclosed by a frame (FIGS. 3 and 4), the frame along each edge of the pane 62 including a ller 63 which has its inner edge in abutment with an edge of the pane 62, a liner 64 which covers the inner surface of the ller 63 and overlaps the inner surface of the pane 62, and a cover member 66, which overlies the forward surface and the outer edge of the filler 63. The forward surface of each filler 63 adjacent the pane 62 is provided with a groove 67, and a flexible retaining molding 68 is positioned within each groove 67 between the filler 63 and the cover member 66, the molding 68 also overlying the forward surface of the pane 62 and holding it in place. The pane 62 may be removed from the frame when desired without the use of tools simply by pulling out the molding 68 and lifting out the pane 62. The filler 63 may be made of wood, the liner 64 is made of a non-corrodable material, and the member 66 is preferably made of metal. The upper edge of member 66 along the lower edge of the frame is preferably bent outwardly and downwardly to form a handle 71 (FIG. 2). A faster 69 (FIG. 4) may be provided at each corner of the frame for holding the cover members 66 together. These fasteners 69 are preferably positioned between the cover members 66 and the fillers 63, and are secured to the cover members 66 as by spot welding. Space for the fasteners 69 is preferably routed out of the llers 63.

The forward portion of the column 44 of each cornerpost 36 and 37 containing the openings 58 is spaced forwardly of its associated angle 41, and the sash 61 is positioned with its vertical side edges within the openings formed between the columns 44 and the angles 41. A spacer channel 50 (FIGS. 3 and 7) is preferably positioned within this opening at the lower end of each cornerpost to hold the angle 41 and the column 44 in proper position.

Along the vertical edges of the sash are fastened a plurality of U-shaped sash guides 72, also made of a noncorrodable material, such as vinyl. The guides 72 are positioned with their arms extending outwardly from the sash and into the openings between the angles 41 and the columns 44 of the cornerposts, and are fastened to the sash 61 as by screws.

The counterbalancing means for the sash 61 comprises a pulley wheel 73 (FIG. 4) pivotally mounted by a pin 74 between a pair of spaced apart pulley supports 47 and 48 (FIGS. 4 and 7) mounted at the upper end of each cornerpost. A cord 76 is looped over each pulley wheel 73 and has one end fastened to a weight 11 and its other end fastened by a screw 78 to a vertical edge of the sash 61. The two weights 77 are preferably sized to hold the sash 61 at any adjusted position, and a guide angle 49 is preferably secured to each outer plate 46 to guide the vert-ical movements of the weights 77.

0n each vertical side of the sash 61 is fastened a sash stop 81 (FIG. 4) including a rubber bumper 82 at its upper end. A strap 83 (FIG. 4) is fastened as by screws to each cornerpost 36 and 37 over the upper end of the opening between the angle 41 and the column 44 for the adjacent vertical edge of the sash 61, the bumpers 82 of the stops 81 engaging the straps 83, when the sash is lifted, and preventing further upward movement of the sash. To remove the sash 61 from the hood the screws holding the straps 83 may be removed, after which the sash 61 may be lifted upwardly out of the front wall of the hood. The sash 61 may also be removed by rst separating one of the cornerposts from the hood and then lifting the sash out.

Air may enter the fume hood through the access opening, the lower bypass opening 55, and the upper bypass opening covered by the grille 39. The ratio of the amount of air entering the access opening to the amount entering the upper by-pass opening may be varied by changing the position of the sash 61. The sash 61 may be used to block off either the access opening or the upper bypass opening or to partially block off both openings. The lower bypass opening 55 is always open for the flow of air into the hood.

The fume hood further includes a light assembly 86 (FIG. 2) for lighting its interior. The light assembly 86 includes a flat sheet 87 of non-corrodable material having an opening 88 formed in it, a pane 90 of glass being positioned over the opening 88. The sheet 87 is secured as by bonding to one side of each of two V-shaped members 89 and 91 along its forward and rearward edges. The other side of the V-shaped member 89 is secured as by bonding to the undersurface of the top panel 32. The lower edge of an angular light cover 92 is secured as by screws 92 to the second V-shaped member 91, and the upper edge of the cover 93 overlies the upper surface of the top panel 32. The two V-shaped members 89 and 91 may also be secured as by bonding or screws to the side walls 16 and 17 if desired. The light assembly 86 further includes a three bulb fluorescent light xture 94 and a bracket 95, which are secured as by welding to the inner surface of the cover 93. Thus, the cover 93 forms an enclosure having an open side, the light fixture 94 being mounted within the enclosure, and the open side being covered by the non-corrodable sheet 97 and glass 9i).

To remove the light assembly from the hood for the purpose of replacing a bulb or for other maintenance, the plate 56 of the front wall 13 is rst removed. The screws 92 are then disconnected and the cover 93 and the light fixture 94 are lifted out.

The fume hood further comprises a bale 101 (FIGS. 2 and 6) pivotally mounted between the access and exhaust openings for regulating the flow of air within the hood. The baffle 101 comprises horizontal support member 102, an upper panel 103 secured at its bottom edge to the member 102 and extending upwardly and toward the front wall 13 from the member 1612, and a lower panel v and the back wall 14 to the exhaust opening.

. vide a scrubbing or ilushing of the side walls.

104 secured at its top edge to the member 102 and extending downwardly from the member 102. The support member 102 is formed with two slots, each extending its entire length, the slots preferably forming an angle of approximately 135 with each other. The bottom and top edges of the upper and lower panels, respectively,

side panels 19 by an adhesive, and a screw 108 (FIG. 3)

may be inserted into the side panels 19 and blocks 106 and 107 while the adhesive is setting if desired. The screws 108 should not however, extend entirely through "the `blocks and into the interior of the superstructure.

The lower surface of the support member 102 is semicircular, and each support block 106 and 107 has a semi- "circular groove formed in it, whichreceivesthe member 102. The width of the two panels 103 and 104 is less than the distance between the panels 19 of the side walls,

Aso that the side edges of the baille panels 103 and 104 are spaced from the side panels 19. The lower baille panel 104has notches formed at its two upper corners to provide clearance for the support blocks 106 and'107.

The baille 101 is thus pivoted about a horizontal axis passing through the center of the semicircular lower sur` face of the support member 102. With reference to FIG. 2, the solid line position of the baille indicates its intermediate position and the two dashed line positions are its lower panel open and lower panel closed positions. In the intermediate position, the top edge of the upper panel 103 is spaced from the top panel 32 and the bottom edge of the lower panel 104 is spaced from both the back panel 28 and the upper surface of the base 11. In the lower panel open position, the upper panel engages the panel 32 of the top wall and the lower panel 104 is spaced a relatively large distance from the back panel 28, and in the lower panel closed position the lower panel 104 engages with the panel 28 of the back wall while the upper `panel 103 is spaced a relatively large distance from the panel 32 of the top wall.

In the event heavier than air fumes are to be exhausted,

`the baille 101 may be pivoted to its lower panel open position where air is prevented from passing over the top edge of the upper panel and ilows through the space between the bottom edge of the lower ypanel and the base 11 Air `also ilows through the spaces between the side edges of the panels 103 and 104 and the side walls 16 and 17 to pro- When lighter than air fumes are to be exhausted, the baille may be moved to its lower panel closed position where most of the air moving to the exhaust opening flows over the top edge of the upper baille panel 103. No air flows past the bottom edge of the lower panel 104 because it engages the panel 28 of the back wall 14.

From FIG. 2 it will be noted that the center of gravity of the baille 101 is to the left of its horizontal axis of rotation because of the forward slant of the upper panel 103, which produces a tendency of the baille 101 to rotate in the counterclockwise direction. To hold the baille in a` selected position, a baille latch 111 is provided (see FIGS. 2 and 5), which is mounted on the back wall 14 and releasibly engages the lower panel 104. The latch 111 cornprises a ratchet block 112 secured as by bonding to the panel 28, the block112 having a plurality of notches 113 formed in its upper surface. The lower panel 104 is provided with a vertical slot 114, the ratchet block 112 being positioned to extend through the slot. A stop block 116 is slidably mounted on the lower panel 104 within the slot 114 above the ratchet block 112, the

cornerpost adjacent each side wall.

stop block 116 having grooves which receive the edges of the panel 104 forming the slot 114. A downwardly extending lip 117is formed on the bottom of the stop block 116, the lip 117 being adapted to extend into a selected one-of the notches in the ratchet block 112. A lift block 118 is attached as by bonding to the stop `block 116, which maybe manually grasped for the purpose of moving the stop block 116 up and down.

When the stop block 116 is in a lowered position, the lip 117 extends into one of the notches 113 of the ratchet block 112 and prevents pivotal movemnt of the baille 101. To adjust the position of the baille, the lift block 118 and the stop block 116 are raised until the ilange 117 clears the ratchet block, the baille 101 is pivoted to the desired position, and the stop block 116 is then lowered to bring the lip 117 into another lone of the notches 113 of the `ratchet block 112. The ratchet block 112 is shown as having five positions, so thatthe baille 101 may be locked in any one of five positions. The notches at the forward and rearward ends of the block 112 are associated with the previously mentioned lower baille `open and closed positions.

FIG. 8 illustrates a fume hood having a diilerent front wall construction and wherein the sash assembly is omitted. The sides, back and top walls of this hood may be the same as the corresponding members of the hood shown in FIG. 1 to 7.

With reference to FIG. 8, the front wall comprises a Each cornerpost comprises a column127 of stepped formation and an outer plate 126 in the form of an angle. Each column 127 extends around the forward and outer sides of the adjacent frame member 18 and is secured thereto by a plurality of bolt and nut assemblies 128. Each plate 126 is secured as by welding to the rearward portion of its associated column 127 and it extends forwardly beyond the column 127.

'A cover 130 is preferably positioned over each cornerpost and is secured to the column 127 and to the outer plate 126 by screws 129 at the vertical sides of the access opening. Above the access opening, a ilat panel (not shown) extends between the cornerposts and is secured to the forward surfaces of the outer plates 126. An upper by-pass opening and grille need not be provided in this construction since a sash assembly is not provided.

A fume hood similar in construction to that shown in FIGS. l to 7 could be made without a sash but in that case the grille 39 would be omitted, or a fume hood similar to that shown in FIGS. l to 7 could have a sash but without the grille 39.

A fume hood having cornerposts similar to that shown in FIG. 8 could have a sash, and in that instance the grille might or might not be used.

Where a non-corrodable material is referred to herein, a composition comprising Portland cement and asbestos ilbers mixed with acid resisting bond and fillers is preferred.

We claim:

` 1. A fume hood as adapted to be positioned on a base,

and comprising front, back, top and two sides walls, said top wall having an exhaust opening formed therein, said front wall comprising a pair of vertical cornerposts adjacent the respective side walls and means connecting the upper portions of said cornerposts, said cornerposts and said connecting means being spaced to form an access opening in the lower portion Iof said front wall, each side wall comprising a generally rectangular side panel of corrosion resistant material and a generally rectangular side frame secured to the outer surface of said side panel, said side frame of each side wall being adjacent and secured to the adjacent one of said cornerposts, said back wall comprising a back panel -of corrosion resistant material overlapping said side frame, means. for securing said back panel to said side frames, and said top wall comprising a top panel of corrosion resistant material positioned on said frame members and overlying the upper edges of said side and back panels, means for securing said top panel to said side frames, said back, top and side panels respectively forming the entire interior surfaces of said back, top and side Walls, whereby the interior surfaces of said back, top and two side walls are completely of corrosion resistant material, at least one of the side panels having a rectangular opening formed therein, a plurality of cleats secured to the outside `of said side panel and extending inwardly the margin of said opening on three sides thereof, and an access panel positioned in and substantially filling said opening, said access panel being formed of a corrosion resistant material, and having a cleat secured to the outside of said access panel and extending beyond an edge of said access panel to -overlie the margin of said opening at the fourth side thereof, and fastening means formed of a corrosion resistant material for releasibly attaching said access panel to one of the cleats secured to the side panel from the interior of the hood.

2. A fume hood adapted to be positioned on a base, and comprising front, back, top and two side walls, said top wall having an exhaust opening formed therein, said front wall comprising a pair of vertical cornerposts adjacent the respective side walls and means connecting the upper portions of said cornerposts, said cornerposts and said connecting means being spaced to form an access opening in the lower portion of said front wall, each side wall cornprising a generally rectangular side panel of corrosion resistant material and a generally rectangular side frame secured to the outer surface of said side panel, said side frame of each side wall being adjacent and secured to the adjacent one of said cornerposts, said back wall comprising a back panel of corrosion resistant material overlapping said side frame, means for securing said back panel to said side frames, and said top wall comprising a top panel of corrosion resistant material positioned on said frame members and overlying the upper edges of said side and back panels, means for securing said top panel to said side frames, said back, top and side panels respectively forming the entire interior surfaces of said back, top and side walls, whereby the interior surfaces of said back, top

- and two side walls are completely of corrosion resistant material, said cornerposts being detachably secured to said connecting means and detachably secured to said side frames, each of said cornerposts comprising a hollow post made up of a plurality of plate members, one of said plate members forming a cover, means for detachably securing said covers to the other members of said cornerposts, said means connecting the upper portions of said cornerposts and said covers being removable from `the front of said hood so that access may be gained to the interior of said hollow cornerposts for detaching said cornerposts from said side frames of said side Walls, whereby said front wall may be detached from said side walls and said side frames will hold said side, back and top panels together in assembled relation.

3. A fume hood as in claim 2, wherein each of said cornerposts has a vertical guide slot formed in the side facing the other cornerpost, said guide slot of each of said cornerposts being formed between two members of said cornerposts, one of said two members being spaced for- Wardly of the other of said two members, the other of said two members of each cornerpost being secured to said :side frame by fasteners, and said one member having lopenings providing access to said fasteners.

4. A fume hood as in claim 2, wherein each of said cornerposts has a vertical guide slot formed on its side facing the other cornerpost, and a sash is slidably mounted with its side edges in said guide slots for movement in a vertical direction, said sash comprising a pane of glass and a frame enclosing said pane of glass, said frame on each edge of said pane of glass comprising a filler positioned against said edge, a liner made of a corrosion resistant material overlying the entire inner surface of said filler and overlapping the inner surface of said pane of glass, a cover overlying the outer surface of said iiller and spaced from the outer surface of said pane of glass, and a ilexible molding positioned between the outer surface of said pane of glass and said cover, said pane of glass being held at each edge by said liner and said molding and being removable when said molding is removed.

5. A fume hood as in claim 4, wherein said cover is spaced from said iiller adjacent each edge of said pane of glass, said molding being positioned within said space.

6. A fume hood as in claim 5, wherein said space is formed by a groove in said illler.

7. A fume hood as in claim 5, wherein the outer dimensions of said pane of glass are less than the inner dimensions of said cover, so that said pane of glass may be withdrawn through said cover.

8. A fume hood as in claim 2, and further including a light assembly mounted at the juncture of said top and front walls, said light assembly being removable from the front of said fume hood when said means connecting the upper portions of said cornerposts of said front wall is removed.

9. A fume hood as in claim 8, wherein said light assembly comprises an enclosure removably secured to said top and side walls, said enclosure having a lower open side, a light fixture mounted within said enclosure, a plate of corrosion resistant material covering said open side and having an opening formed therein, and a pane of glass covering said opening.

10. A fume hood adapted to be positioned on a base and comprising front, back, top and two side walls secured together in a boxlike conilguration, said top wall'having an exhaust opening formed therein adapted to be connected to an exhaust duct, and said front wall having an access opening formed therein, a baille positioned within the hood between said access and exhaust openings, means adjacent said back wall for pivotally mounting said baille about a horizontal axis intermediate the upper and lower edges of said baille, said baffle comprising a horizontally extending support member supported by said mounting means, an upper panel having an edge secured to said member and extending upwardly toward said top wall, and a lower panel having an edge secured to said member and extending downwardly toward said base, and manually operable latch means connecting one of said walls and one of said panels for releasably holding said baille against movement, said panel having a vertical slot formed therein, and said latch comprising a ratchet block secured to said back wall and extending forwardly through said slot, said lower ratchet block having a plurality of notches formed in its upper surface, and a stop block within said slot above said ratchet block is slidably mounted for movement in a vertical direction, said stop block having a lip formed thereon selectively engageable in said notches of said ratchet block to hold said baille in adjusted positions.

11. A fume hood as in claim 10, wherein said stop block has grooves formed in its opposite sides, the vertical edges of said slot extending into said grooves of said stop block.

References Cited by the Examiner UNITED STATES PATENTS 2,550,300 4/ 1951 Schunk. 2,702,505 2/ 1955 Nelson. 2,704,505 3/ 1955 Morrison. 3,004,305 10/ 1961 Goodemote. 3,111,077 11/1963 Cortright.

ROBERT A. OLEARY, Primary Examiner, 

1. A FUME HOOD AS ADAPTED TO BE POSITIONED ON A BASE, AND COMPRISING FRONT, BACK, TOP AND TWO SIDES WALLS, SAID TOP WALL HAVING AN EXHAUST OPENING FORMED THEREIN, SAID FRONT WALL COMPRISING A PAIR OF VERTICAL CORNERPOSTS ADJACENT THE RESPECTIVE SIDE WALLS AND MEANS CONNECTING THE UPPER PORTIONS OF SAID CORNERPOSTS, SAID CORNERPOSTS AND SAID CONNECTING MEANS BEING SPACED TO FORM AN ACCESS OPENING IN THE LOWER PORTION OF SAID FRONT WALL, EACH SIDE WALL COMPRISING A GENERALLY RECTANGULAR SIDE PANEL OF CORROSION RESISTANT MATERIAL AND A GENERALLY RECTANGULAR SIDE FRAME SECURED TO THE OUTER SURFACE OF SAID SIDE PANEL, SAID SIDE FRAME OF EACH SIDE WALL BEING ADJACENT AND SECURED TO THE ADJACENT ONE OF SAID CORNERPOSTS, SAID BACK WALL COMPRISING A BACK PANEL OF CORROSION RESISTANT MATERIAL OVERLAPPING SAID SIDE FRAME, MEANS FOR SECURING SAID BACK PANEL TO SAID SIDE FRAMES, AND SAID TOP WALL COMPRISING A TOP PANEL TO CORROSION RESISTANT MATERIAL POSITIONED ON SAID FRAME MEMBERS AND OVERLYING THE UPPER EDGES OF SAID SIDE AND BACK PANELS, MEANS FOR SECURING SAID TOP PANEL TO SAID SIDE FRAMES, SAID BACK, TOP AND SIDE PANELS RESPECTIVELY FORMING THE ENTIRE INTERIOR SURFACES OF SAID BACK, TOP AND SIDE WALLS, WHEREBY THE INTERIOR SUR- 